Exploring the divergent effects of Mo and W dopants in transition metal phosphides: Mechanistic insights and heterostructure contributions to hydrogen evolution

Cobalt-based phosphides (Co x P y ) are promising for hydrogen evolution reaction (HER) due to the Co P synergistic effect, which enhances electron density, charge transfer, and conductivity. However, their fixed electronic structure limits redox properties, reducing catalytic performance at high currents. Herein, we compare the doping effects of Mo and W, whose orbital structures resemble Ru and Ir, to explore bifunctional catalytic mechanisms, particularly HER, and enhance Co x P y 's tunability and conductivity under high current conditions by leveraging flexible valence states of Mo and W, especially W 6+ with vacant orbitals. Either W or Mo dopant facilitates charge transfer within CP@CC, influencing electron distribution and catalytic performance. Mo, with lower-energy d-electrons, adsorbs more electrons, while W enhances orbital hybridization with P, increasing electron density around W. Mo or W incorporation into CoP forms CoP/Co 2 P heterostructures, with W-CoP/Co 2 P exhibiting superior acidic HER activity at 500 mA cm −2 . This results from W 6+ with vacant orbitals having a higher electron-adsorption capacity, which enhances the effectiveness of P ions as the active sites by lowering H ⁎ adsorption free energy. This work highlights that Mo’s lower-energy d-electrons and W's vacant orbitals drive charge redistribution, enhancing HER performance under high current, offering insights for catalyst design with similar electronic structures. • Mo/W doping overcomes fixed electronic structure and poor redox properties limiting Co x P y HER efficiency at high currents. • Doping induces charge redistribution and CoP/Co 2 P heterostructure formation, boosting catalytic activity and stability under high-current HER. • W doping significantly outperforms Mo doping at high current densities (e.g., 500 mA·cm −2 ) due to stronger W 6+ -P orbital hybridization and electron adsorption. • W 6+ vacant orbitals optimize H ⁎ adsorption free energy, enhancing acidic HER kinetics and providing design principles for efficient Mo/W-doped electrocatalysts.